This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for SOLAR CELL AND METHOD FOR MANUFACTURING THE SAME earlier filed in the Korean Industrial Property Office on Jan. 3, 2001 and there duly assigned Serial No. 2001-253.
1. Field of the Invention
The present invention relates to a solar cell and more particularly a solar cell having high efficiency.
2. Description of the Related Art
A pn junction solar cell includes a junction of a p-type semiconductor and an n-type semiconductor. In the cell, electron-holepairs are generated by photons. The generated electrons and holes respectively move toward the p-type and n-type semiconductors, and then accumulated in two contacts. When light shining on the solar cell produces both a current and a voltage, the light-generated current and voltage can be used as electric power.
In a solar cell, n-type and p-type impurities are doped on the front and rear surfaces of a silicon substrate for making the p-n junction and contacts are formed on both surfaces. To fabricate such a solar cell, oxide layers are formed and etched with predetermined patterns by costly photolithography process on each surface of a Si substrate, and impurities are doped through the patterned area. Then, contact layers are formed on the patterned area.
U.S. Pat. No. 4,082,568 issued to Lindmayer for Solar Cell with Multiple-metal Contacts and U.S. Pat. No. 4,124,455 issued to Lindmayer for Method of Making Solar Cell with Multiple-metal Contacts disclose a technique for fabricating such a solar cell, in which a front contact is formed of a multi-layered metal pattern including Ti-based metal and Pd-based metal to prevent conductive material of the front contact from diffusing into the silicon substrate.
U.S. Pat. No. 4,278,704 issued to Williams for Method for Forming an Electrical Contact to a Solar Cell discloses a method of forming an electrical contact of a solar cell by using a silicide to lower the contact resistance.
The multi-layered metal pattern including Ti-based metal and Pd-based metal is formed by evaporation method accompanying photolithography in which the multi-layered metal deposited on the portion except the contact area is eliminated. The photolithography is costly and not appropriate for mass production. In addition, the Ti-based metal and Pd-based metal is costly and the formation of the multi-layered metal pattern is complicated.
Furthermore, a conventional front contact includes a common electrode connected with a contact pad, and finger electrodes extending from the common electrode with uniform width. The light absorption rate of the solar cell is reduced as much as the area of the front contact. That is, the greater the front contact occupies an area, the more the shading loss occurs.
Japanese Patent Laid-Open No. 1994-283736 issued to Shibuya et al. for a Solar Cell discloses a solar cell having a front electrode of which the cross-sectional areas become larger as it goes from an edge to a terminal. However, the front electrode being consisted of Ti/Pd/Ag is formed by costly photolithography process and lift-off process. In addition, the front contact pattern and the front electrode are manufactured by photolithography process, and therefore they have the same shape.
Therefore, there is a need for a solar cell that can improve the energy conversion efficiency by minimizing the shading loss, while reducing the manufacturing costs.
It is therefore an objective of the present invention to provide a solar cell that can be fabricated by simple manufacturing process and have the minimized manufacturing costs.
It is another objective of the present invention to provide a solar cell showing the improved energy conversion efficiency by minimizing the shading loss, while reducing the manufacturing costs.
To meet the above and other objectives, the present invention provides a pn junction solar cell including a pn junction structure including a p-type and an n-type semiconducting layer, a front contact electrode formed on the front surface of the pn junction structure, the front contact electrode being reduced in a width as it goes away from a terminal, and a rear contact electrode formed on a rear surface of the pn structure. According to a feature of the present invention, at least one of the p-type and n-type semiconducting layer is formed of Si.
According to another feature of the present invention, a plurality of the front contact electrode make branches being arranged in an identical direction, and the branches are collected at a common electrode which electrically interconnects proximal ends of the branches and a front electrode terminal.
According to yet another feature of the present invention, a shape of the front contact electrode is a triangle.
According to still yet another feature of the present invention, the solar cell may further include a buffer formed between the front surface of the pn junction structure and the front contact electrode. According to still yet another feature of the present invention, the buffer is formed of a material selected from the group including Ni, Cr, Co and Ti.
According to still yet another feature of the present invention, the buffer includes an interfacial silicide layer.
According to still yet another feature of the present invention, the front and rear contact electrodes are formed of Cu or Ag.
According to still yet another feature of the present invention, a solar cell may further include a Ti/Pd (Ti or Pd or both Ti and Pd) layer formed between the rear contact electrode and rear surface.